1. Field of the Invention
The present invention relates to an optical wavelength converter device, and more particularly, to an optical wavelength converter device in the form of a three-dimensional optical waveguide which is made of a semiconductor material, and a method of manufacturing such an optical wavelength converter device.
2. Description of the Prior Art
Various attempts have heretofore being made to convert the wavelength of a laser beam into a second harmonic (i.e. to shorten the wavelength of a laser beam), using a nonlinear optical material. One well known example of an optical wavelength converter device for effecting such laser wavelength conversion is in the form of a three-dimensional optical waveguide. This optical wavelength converter device comprises a glass substrate serving as a cladding and a waveguide element embedded in the glass substrate. The waveguide element is made of a nonlinear optical material having a refractive index which is higher than the refractive index of the glass substrate. As with a fiber-type optical wavelength converter device, the three-dimensional optical waveguide serving as an optical wavelength converter device can convert the wavelength of a fundamental wave of high intensity into a second harmonic with a high efficiency.
However, since the cladding is made of glass, it is highly difficult to embed the waveguide element fully in the cladding. Therefore, in most optical wavelength converter devices of this type, the waveguide element is embedded in a groove defined in one surface of the glass substrate. According to this waveguide structure, a portion of the waveguide element is not covered with the cladding. Because the wavelength-converted wave which is emitted from the end face of this optical wavelength converter device is a beam having a substantially crescent-shaped cross section, the beam cannot be converged into a sufficiently small beam spot.